In recent years, because of the availability of superconducting magnets there has been increasing interest in strong magnetic fields, for example, magnetic fields in excess of one Tesla, that are easily obtained with such magnets. This in turn has created a need for detectors for convenient measurement of such strong fields. An ideal detector should have a number of characteristics. It should be simple to use and relatively inexpensive. It should be small so that it can be used as a probe to permit a high degree of spatial resolution of magnet flux, as is necessary when one wishes to plot accurately the field distribution associated with a particular magnetic structure. It should also have a high sensitivity, that is relatively independent of temperature over a wide range. While specific detectors are available that have one or more of these characteristics, in none are all these characteristics present to the extend desired.
In a paper published in IEEE Transections on Electron Devices Vol. 36, No. 9 September 1989 pps. 1639-1643, entitled "Highly Sensitive Split Contact Magnetoristor with AlAs/GaAs Superlattice Structures", there is described a modulation-doped AlAs/GaAs superlattice grown on a semi-insulating GaAs substrate that was provided with a first electrode at one surface and a split electrode at the other surface to form essentially a pair of parallel electrodes. The device is positioned so that the magnetic field extends through the superlattice parallel to the planes of the alternating layers. The Hall effect then creates a difference between the currents flowing in the two spaced electrodes and this difference is related to the strength of the magnetic field. This detector was described as effective to measure magnetic fields up to an intensity of about one Tesla. In this structure, the sensitivity increased with the thickness of the superlattice, decreased with the cross-section of the superlattice, and decreased with the separation of the two split contacts. The need for the split contact tends to make it difficult to achieve an especially small cross sectional area for the superlattice, as is generally desirable for fine resolution of any spatial distribution of the measured field. Also the detection of differential currents adds to circuit complexity. The present invention provides a detector of better characteristics in these respects.